I filled up with gas this morning, the gas light is still on and it said full tank and then it shows empty tank and the gas light came back on. I hae tried several times to put the gas cap back on.

Grounding is very important with sensors, especially with fuel systems. Your sensors could be defective as believe it or not, they do wear out or your float is sticking

If you cannot fill the tank because of an erroneous reading then it is time to replace the gas gauge sending unit responsible for the anomaly. Hope fully you can do it from the trunk - otherwise you will have to drop the gas tank to gain access.

Either the fuel tank sender in the tank is bad and needs replacement, or the fuel gauge is faulty. I would bet the one in the tank is probably bad, because that's usually the case. Find the connection at the fuel tank, disconnect it and use a VOM to get a resistance reading while the tank is empty and reading 1/2. It should match the specs.

If you need further help, reach me via phone at https://www.6ya.com/expert/daniel_4061c3d97c12c4c7

It sounds as if the fuel tank sending unit is faulty. This is a small float connected to a variable resistor on the fuel pump/sending unit assembly. Unfortunately this assembly is fairly expensive (over $300) and the fuel tank may need to be removed to replace it.

sounds like the fuel sending unit in the gas tank

faulty feul sending unit or bad ground will need to use a meter to test the system

there is a fuel senor inside of the tank and it could very well be the problem

Replace the fuel sensor / sending unit, it is inside the gas tank, it is a lot of work to drop the gas tank, I have done it on other cars... If you want to do it make sure the tank is almost empty it is very heavy with all that gas inside make sure there is no open flames or cigarretes close
Good Luck

Unfortunately this is most likely the fuel pump module, which includes the fuel level sensor also. This should be diagnosed more thoroughly with a scanner, a good scanner will be able to check instrument cluster separately to confirm the gage is working right,and check for trouble codes that may not light any warning lamps. Hope this helps. Rate me please.P.S. Dont use that fuel station any more.

Yes it is all one unit, and yes that is what the problem is. don't use aftermarket parts, use OEM, (Delco Remy) they are much better quality.